全文获取类型
收费全文 | 1577篇 |
免费 | 9篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 1篇 |
化学工业 | 67篇 |
金属工艺 | 2篇 |
机械仪表 | 3篇 |
建筑科学 | 9篇 |
能源动力 | 12篇 |
轻工业 | 10篇 |
水利工程 | 3篇 |
石油天然气 | 1篇 |
无线电 | 13篇 |
一般工业技术 | 16篇 |
冶金工业 | 1428篇 |
自动化技术 | 23篇 |
出版年
2023年 | 2篇 |
2019年 | 2篇 |
2018年 | 3篇 |
2017年 | 3篇 |
2015年 | 5篇 |
2013年 | 10篇 |
2012年 | 3篇 |
2011年 | 8篇 |
2010年 | 8篇 |
2009年 | 4篇 |
2008年 | 11篇 |
2007年 | 6篇 |
2005年 | 4篇 |
2004年 | 8篇 |
2003年 | 7篇 |
2002年 | 7篇 |
2001年 | 5篇 |
2000年 | 5篇 |
1999年 | 44篇 |
1998年 | 403篇 |
1997年 | 241篇 |
1996年 | 174篇 |
1995年 | 83篇 |
1994年 | 84篇 |
1993年 | 72篇 |
1992年 | 21篇 |
1991年 | 26篇 |
1990年 | 30篇 |
1989年 | 10篇 |
1988年 | 18篇 |
1987年 | 24篇 |
1986年 | 14篇 |
1985年 | 15篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 12篇 |
1981年 | 13篇 |
1980年 | 13篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 53篇 |
1976年 | 108篇 |
1975年 | 2篇 |
1965年 | 1篇 |
1957年 | 1篇 |
1944年 | 1篇 |
1941年 | 1篇 |
1940年 | 2篇 |
1938年 | 1篇 |
1928年 | 1篇 |
排序方式: 共有1588条查询结果,搜索用时 359 毫秒
51.
52.
OBJECTIVES: This study assessed the effectiveness of a family planning intervention with and without husband's participation in reducing pregnancy and abortion rates in Shanghai, China. METHODS: In this 3-arm randomized trial among 1800 nonsterilized married women, educational interventions targeting both spouses and targeting the wife only were compared with usual family planning care. RESULTS: Among women not using intrauterine devices (IUDs), the intervention with husband's participation had an effect in reducing pregnancy rates (adjusted odds ratio [OR] = 0.36, 95% confidence interval [CI] = 0.12, 1.1) and abortion rates (adjusted OR = 0.29, CI = 0.09, 0.94) compared with control subjects, and a significant effect in reducing pregnancy rates (adjusted OR = 0.29, CI = 0.10, 0.85) and abortion rates (adjusted OR = 0.24, CI = 0.07, 0.77) compared with wife-only subjects. CONCLUSIONS: Family planning interventions involving husbands may reduce pregnancy and abortion rates among non-IUD users. 相似文献
53.
Sixty cats which underwent an ovariohysterectomy were randomly allocated into four treatment groups. One group (controls) received no analgesics postoperatively, and the others received either a single dose of buprenorphine (0.006 mg/kg) intramuscularly, or pethidine (5 mg/kg) intramuscularly, or ketoprofen (2 mg/kg) subcutaneously. The analgesia obtained after each treatment was assessed by three measures. There were significant differences between the groups both for the requirement for intervention analgesia (P = 0.0008) and for the overall clinical assessment (P = 0.0003) with ketoprofen requiring least intervention analgesia and having the best overall clinical assessment, followed by buprenorphine then pethidine. The control group required the most intervention analgesia and had the worst overall clinical assessment. Visual analogue scale scoring for pain produced significant differences between the groups from one hour after the operation, with the cats which were given ketoprofen tending to have lower pain scores than the other groups. 相似文献
54.
Magnetic resonance spectroscopy (MRS), an application of the methods of nuclear magnetic resonance (NMR), is a functional imaging modality that provides a view of localized biochemistry in vivo. A number of studies applying MRS to the neurochemistry of schizophrenia have been reported, which encompass a range of patient populations, states of medication, anatomic regions, nuclear species, and MRS techniques. A brief review of the history and methodology of NMR and MRS is presented. Comparison is made of MRS capabilities with other functional imaging modalities. Aspects of the neurochemistry of schizophrenia relevant to MRS studies are reviewed, as are the reported MRS studies involving patients with schizophrenia. Areas of consistent findings include decreased phosphomonoesters and increased phosphodiesters in frontal lobes, and decreases in the putative neuronal cell marker, N-acetylaspartate, in temporal lobes. Studies of neurotransmitters such as glutamate, gamma-aminobutyric acid, and glutamine have generated inconsistent results. New insights into alterations in neurochemistry in schizophrenia have been provided by MRS. Studies of neurotransmitters have future potential with improvements in field strength and in spectral editing techniques. MRS has the potential to measure brain medication levels and simultaneous effects on neurochemistry. MRS may assist in characterizing high-risk populations, and ultimately guide medication use. 相似文献
55.
LS Jeong G Buenger JJ McCormack DA Cooney Z Hao VE Marquez 《Canadian Metallurgical Quarterly》1998,41(14):2572-2578
Three carbocylic analogues of the potent cytidine deaminase inhibitor (CDA) zebularine [1-(beta-D-ribofuranosyl)-1, 2-dihydropyrimidin-2-one, 1a] were synthesized. The selected pseudosugar templates correspond, respectively, to the cyclopentenyl moiety of neplanocin A (compound 4), the cyclopentyl moiety of aristeromycin (compound 5), and a newly designed, rigid bicyclo[3.1. 0]hexane moiety (compound 6). These three carba-nucleoside versions of zebularine were fashioned to overcome the inherent instability of the parent drug. Each target compound was approached differently using either convergent or linear approaches. The immediate precursor to the cyclopentenyl analogue 4 was obtained by a Mitsunobu coupling of pseudosugar 7 with 2-hydroxypyrimidine. The cyclopentyl analogue 5 was linearly constructed from carbocyclic amine 17, and the final target 6 was similarly constructed from the carbobicyclic amine 27. Of the three target compounds, only 5 showed a significant level of inhibition against human CDA, but it was 16 times less potent than zebularine (Ki = 38 microM vs Ki(apparent) = 2.3 microM). Although these carbocyclic analogues appeared to be more stable than zebularine, replacement of the electronegative CO4' oxygen for the less electronegative carbon in 4-6 presumably reduces the capacity of the pyrimidin-2(1H)-one ring to form a covalent hydrate, a step considered crucial for the compound to function as a transition-state inhibitor of the enzyme. 相似文献
56.
MJ Camp JR Wingard CE Gilmore LS Lin SP Dix TG Davidson RB Geller 《Canadian Metallurgical Quarterly》1998,42(12):3103-3106
This study evaluated the efficacy of low-dose dopamine for prevention of amphotericin B-induced nephrotoxicity in autologous bone marrow transplant and leukemia patients. Seventy-one patients undergoing cytoreductive therapy who required amphotericin B were randomly assigned in an unblinded fashion to a group receiving continuous-infusion low-dose dopamine (3 microgram/kg/min) or a group receiving no dopamine. Amphotericin B was dosed at 0.5 or 1.0 mg/kg/day based on computerized tomography scan results or presence of positive blood cultures. No patient received saline boluses. The rate of nephrotoxicity, severity as graded by Southwest Oncology Group toxicity criteria, and time to each grade of nephrotoxicity were compared between the two groups. Eighty percent of the no-dopamine group and 66.7% of the dopamine group developed nephrotoxicity, defined as a 1.5-fold or greater increase in baseline serum creatinine level (P = 0.20). No statistical difference was noted at any grade of nephrotoxicity between the two groups. Thirty-four percent of patients in the no-dopamine group versus 17.6% in the dopamine group had a 2.5-fold or greater increase in serum creatinine level, which was not statistically significant (P = 0.0888). Ten patients developed grade IV nephrotoxicity and were withdrawn from the study, 7 in the no-dopamine group and 3 in the dopamine group (P = 0.19). The time to each grade of nephrotoxicity was also not significantly different for the two groups. Eleven adverse drug reactions were reported in the dopamine group in comparison to one in the no-dopamine group. Thus, dopamine offers little in the way of prevention of nephrotoxicity associated with amphotericin B therapy. Although the significance of drug reactions in the dopamine group is not clearly established due to lack of cardiac monitoring in the no-dopamine group, dopamine therapy is not without complications. 相似文献
57.
Making mistakes when predicting shifts in species range in response to global warming 总被引:1,自引:0,他引:1
AJ Davis LS Jenkinson JH Lawton B Shorrocks S Wood 《Canadian Metallurgical Quarterly》1998,391(6669):783-786
Many attempts to predict the biotic responses to climate change rely on the 'climate envelope' approach, in which the current distribution of a species is mapped in climate-space and then, if the position of that climate-space changes, the distribution of the species is predicted to shift accordingly. The flaw in this approach is that distributions of species also reflect the influence of interactions with other species, so predictions based on climate envelopes may be very misleading if the interactions between species are altered by climate change. An additional problem is that current distributions may be the result of sources and sinks, in which species appear to thrive in places where they really persist only because individuals disperse into them from elsewhere. Here we use microcosm experiments on simple but realistic assemblages to show how misleading the climate envelope approach can be. We show that dispersal and interactions, which are important elements of population dynamics, must be included in predictions of biotic responses to climate change. 相似文献
58.
MC Munin TE Rudy NW Glynn LS Crossett HE Rubash 《Canadian Metallurgical Quarterly》1998,279(11):847-852
CONTEXT: Inpatient rehabilitation after elective hip and knee arthroplasty is often necessary for patients who cannot function at home soon after surgery, but how soon after surgery inpatient rehabilitation can be initiated has not been studied. OBJECTIVE: To test the hypothesis that high-risk patients undergoing elective hip and knee arthroplasty would incur less total cost and experience more rapid functional improvement if inpatient rehabilitation began on postoperative day 3 rather than day 7, without adverse consequences to the patients. DESIGN: Randomized controlled trial conducted from 1994 to 1996. SETTING: Tertiary care center. PARTICIPANTS: A total of 86 patients undergoing elective hip or knee arthroplasty and who met the following criteria for being high risk: 70 years of age or older and living alone, 70 years of age or older with 2 or more comorbid conditions, or any age with 3 or more comorbid conditions. Of the 86 patients, 71 completed the study. INTERVENTIONS: Random assignment to begin inpatient rehabilitation on postoperative day 3 vs postoperative day 7. MAIN OUTCOME MEASURES: Total length of stay and cost from orthopedic and rehabilitation hospital admissions, functional performance in hospitals using a subset of the functional independence measure, and 4-month follow-up assessment using the RAND 36-item health survey I and the functional status index. RESULTS: Patients who completed the study and began inpatient rehabilitation on postoperative day 3 exhibited shorter mean (+/-SD) total length of stay (11.7+/-2.3 days vs 14.5+/-1.9, P<.001), lower mean (+/-SD) total cost ($25891+/-$3648 vs $27762+/-$3626, P<.03), more rapid attainment of short-term functional milestones between days 6 and 10 (36.2+/-14.4 m ambulated vs 21.4+/-13.3 m, P<.001; 4.8+/-0.8 mean transfer functional independence measure score vs 4.3+/-0.7, P<.01), and equivalent functional outcome at 4-month follow-up. CONCLUSION: These data showed that high-risk individuals were able to tolerate early intensive rehabilitation, and this intervention yielded faster attainment of short-term functional milestones in fewer days using less total cost. 相似文献
59.
Experimental data from protein engineering studies and NMR spectroscopy have been used by theoreticians to develop algorithms for helix propensity and to benchmark computer simulations of folding pathways and energy landscapes. Molecular dynamic simulations of the unfolding of chymotrypsin inhibitor 2 (CI2) have provided detailed structural models of the transition state ensemble for unfolding/folding of the protein. We now have used the simulated transition state structures to design faster folding mutants of CI2. The models pinpoint a number of unfavorable local interactions at the carboxyl terminus of the single alpha-helix and in the protease-binding loop region of CI2. By removing these interactions or replacing them with stabilizing ones, we have increased the rate of folding of the protein up to 40-fold (tau = 0.4 ms). This correspondence, and other examples of agreement between experiment and theory in general, Phi-values and molecular dynamics simulations, in particular, suggest that significant progress has been made toward describing complete folding pathways at atomic resolution by combining experiment and simulation. 相似文献
60.
The present study was designed to investigate the mechanism through which leucine and histidine regulate translation initiation in L6 myoblasts. The results show that both amino acids stimulate initiation and coordinately regulate the activity of eukaryotic initiation factor eIF2B. The changes in eIF2B activity could be explained in part by modulation of the phosphorylation state of the alpha-subunit of eIF2. The activity changes might also be a result of modulation of the phosphorylation state of the eIF2B epsilon-subunit, because deprivation of either amino acid caused a decrease in eIF2Bepsilon kinase activity. Leucine, but not histidine, additionally caused a redistribution of eIF4E from the inactive eIF4E.4E-BP1 complex to the active eIF4E.eIF4G complex. The redistribution was a result of increased phosphorylation of 4E-BP1. The changes in 4E-BP1 phosphorylation and eIF4E redistribution associated with leucine deprivation were not observed in the presence of insulin. However, the leucine- and histidine-induced alterations in global protein synthesis and eIF2B activity were maintained in the presence of the hormone. Overall, the results suggest that both leucine and histidine regulate global protein synthesis through modulation of eIF2B activity. Furthermore, under the conditions employed herein, alterations in eIF4E availability are not rate-controlling for global protein synthesis but might be necessary for regulation of translation of specific mRNAs. 相似文献